1. Field of the Invention
This invention relates to static magnetic card readers and control systems for electrically operable apparatus, e.g., doors, turnstiles, printers, etc.
2. Discussion of the Prior Art
Static card readers are known which employ a plurality of stationary electromagnet sensors, and which are adapted to receive and hold a spot magnetized card. Sensor coils are pulsed to develop logic level signals representing the polarity distribution of the card spots, and hence the code of the card. See U.S. Pat. Nos. 3,686,479 and 3,885,130, assigned to the same assignee as the present application.
Where such readers are provided at various doors throughout a building, it is known to incorporate all readers into an on-line system wherein they are queried from a station query and stored data comparison console. When a card is inserted in a reader at a particular location, on the next query the code data in the card is transmitted to the console for comparison with stored data. If there is a match, the console transmits a "go" command pulse to the reader so as to enable it for energizing the relay or solenoid for the door strike at that location. If there is no match, a "no-go" signal is transmitted which may be the termination of a query pulse or equivalent wide pulse that prevents operation of logic circuitry to enable the reader for actuating the door strike.
Heretofore, when the console failed to operate in such a system, i.e., to query and send command pulses, the security represented by the system was completely lost. The fact of failure is instantly known, and it has been necessary for security personnel to man the different locations for identifying, and opening doors to permit entry of, authorized persons.